Motor driven linear actuators are well known in the art and used in a variety of applications, such as industrial machinery, precision machine tools, electronic machinery, transport machinery, and etc. The motor driven linear actuator conventionally converts the rotary motion of an electric motor to linear motion by using a ballscrew device.
FIG. 1 is a schematic longitudinal cross-sectional view showing a conventional motor driven linear actuator. The conventional motor driven linear actuator 1 includes an electric motor 11, a ballscrew device 12, a coupling 13, a frame 14, a bearing 15, and a fixing carriage-nut 16. The electric motor 11 includes a rotor 111, a stator 112, and a motor shaft 113. The motor shaft 113 is disposed in the rotor 111. The rotor 111 includes a plurality of permanent magnets 114 thereon, and the stator 112 includes windings which carry currents that interact with the magnetic field of the permanent magnets 114 of the rotor 111, so that a driving force is generated to turn the motor shaft 113 of the rotor 111. Preferably, the electric motor 11 is a servo motor.
The ballscrew device 12 is disposed in the frame 14 and includes a screw 121, a carriage-nut 122, a table 123, a linear bearing 124 and a supporting bearing 125. One end portion of the screw 121 of the ballscrew device 12 is coaxially connected to the motor shaft 113 of the electric motor 11 via the coupling 13. Namely, the coupling 13 is interconnected with the motor shaft 113 of the electric motor 11 and the screw 121 of the ballscrew device 12 for allowing the screw 121 of the ballscrew device 12 to be rotated according to the rotation motion of the motor shaft 113 of the electric motor 11. The carriage-nut 122 is threadably engaged with the screw 121, and the table 123 is fixed to the carriage-nut 122 for carrying a load thereon. The carriage-nut 122 incorporates rolling elements (not shown), such as balls, between the screw 121 and the carriage-nut 122. Consequently, a motor driven linear actuator with high load transfer and long life can be achieved. The linear bearing 124 is connected with the carriage-nut 122 and disposed in the frame 14 for holding the carriage-nut 122 in a non-rotatable state and guiding the carriage-nut 122 to move in a linear direction. Consequently, the carriage-nut 122 is moved along the screw 121 when the screw 121 of the ballscrew device 12 is rotated by the driving of the electric motor 11. The supporting bearing 125 is disposed in the frame 14 and configured to support the other end portion of the screw 121 of the ballscrew device 12, so that the end portion of the screw 121 is axially immovably relative to the frame 14.
When the motor shaft 113 of the electric motor 11 and the screw 121 of the ballscrew device 12 are coupled together via the coupling 13, a bearing 15 is employed to radially support the end portion of the screw 121, so that the rigidity of the electric motor 11 can be increased. In addition, a fixing carriage-nut 16 is fixed on the screw 121 and located between the coupling 13 and the bearing 15 for applying a pre-pressure on the bearing 15 and limiting the bearing 15 to move in an axial direction relative to the screw 121.
The conventional motor driven linear actuator 1 employs a coupling 13 to couple the motor shaft 113 of the electric motor 11 and the screw 121 of the ballscrew device 12 together. However, the rigidity of the coupling 13 is weak. Consequently, the rigidity of the motor driven linear actuator 1 is degraded, and the response speed of the motor driven linear actuator 1 can't be promoted. In addition, in order to secure the bearing 15, a fixing carriage-nut 16 must be fixed on the screw 121 and located between the coupling 13 and the bearing 15 for applying a pre-pressure on the bearing 15 and limiting the bearing 15 to move in an axial direction relative to the screw 121. Consequently, the coupling structure between the motor shaft 113 of the electric motor 11 and the screw 121 of the ballscrew device 12 is complex, the space for coupling the motor shaft 113 of the electric motor 11 and the screw 121 of the ballscrew device 12 is increased, and the whole length of the motor driven linear actuator 1 is increased.
Therefore, there is a need of providing a motor driven linear actuator and an electric motor thereof to obviate the drawbacks encountered from the prior arts.